hydrogen peroxide

Accepted Manuscript Title: Removal of Carbofuran in aqueous solution by using UV-irradiation/hydrogen peroxide Authors: Khalid Elmamoun Ahmed Ibrahim, Dilek S¸olpan PII: DOI: Reference:

S2213-3437(18)30743-7 https://doi.org/10.1016/j.jece.2018.102820 JECE 102820

To appear in: Received date: Revised date: Accepted date:

10 September 2018 28 November 2018 1 December 2018

Please cite this article as: Ahmed Ibrahim KE, S¸olpan D, Removal of Carbofuran in aqueous solution by using UV-irradiation/hydrogen peroxide, Journal of Environmental Chemical Engineering (2018), https://doi.org/10.1016/j.jece.2018.102820 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Removal of Carbofuran in aqueous solution by using UV-irradiation/hydrogen peroxide

Khalid Elmamoun Ahmed Ibrahim*1, Dilek Şolpan2 1

Department of Radiation Processing, Sudan Atomic Energy Commission, Post code:

Hacettepe University, Department of Chemistry, 06800, Beytepe-Ankara/TURKEY

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11111, P.O.Box:3001 Khartoum, SUDAN

Highlights

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Abstract

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Degradation of Carbofuran in aqueous solutions by using UV and UV/H2O2 was evaluated. The intermediates, aliphatic acids, ions, and final product (s) was determined by GC-MS and IC. The degradation pathway was proposed. Investigation of synergic effect for UV and UV/H2O2 process.

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Pesticide residues in natural water are one of the biggest environmental problems. carbofuran is an insecticide widely used in agricultural activities and it is easily

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biodegradable. Although this compound has a relatively short lifetime in soils and its persistence in the environment varies from one to several weeks. For this reason, the elimination of carbofuran residual from contaminated waters using suitable technique is of environmental interest. The aim of this study to investigate the synergetic effect of UV and UV with hydrogen peroxide on the degradation of carbofuran in aqueous

solution. 50 mgL-1 aqueous solutions of carbofuran (CBF) were prepared. The solutions were exposed to various UV irradiation times. The irradiation time varied from (15-240 min). Hydrogen peroxide was set at 4.8 mM as a minimum concentration level. To follow the degradation percent, formaldehyde concentration, and to identify the intermediates by-products, GC-MS, IC, and UV-Visible

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spectrophotometer were used. The pH, total acidity, and dissolved oxygen values

were determined before and after treatment with UV irradiation with/without

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hydrogen peroxide. Depending on the results obtained the mechanism pathway

(degradation) was suggested. The complete removal of carbofuran in aqueous solution

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took place at 180 min in the presence of H2O2.

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Key Words

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Carbofuran, advanced oxidation processes (AOP’s), UV/H2O2, hydrogen peroxide

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effect. 1. Introduction

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The availability of clean water plays an important role in the economic, social, religious and cultural development of societies. So, it is necessary to protect water

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sources as clean as possible [1]. Drinking water is contaminated by more than one method, including accidental transfer from neighboring areas during the spraying

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process, or from leakage from land dealing with pesticides in conjunction with water movement, or direct pollution by using pesticides in the elimination of plants, therefore pesticide residues are a serious problem both for human health and animals [2, 3]. In recent years, scientists and decision-makers have been concerned about the

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effects of the indiscriminate use of pesticides on human and animal health [4]. Recently, a different group of researchers has an advanced novel method in order to resolve the obstacles in wastewater treatment method. Sepehri and Sarrafzadeh, advanced pioneering strategy for fouling mitigation and nitrification enhancement through enrichment of nitrifiers community in membrane bioreactor [5].

Carbofuran is one of the chemical pesticides that has widely been used in recent years for its high effectiveness in controlling insects and worms that spoil crops, fruits, and vegetables [6]. Some studies confirmed the presence of carbofuran in surface and ground water [7, 8]. pH is the most influential factor on the efficiency of decomposition of carbofuran in water. For instance, it was found that the half-life is

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more than five weeks in alkaline medium and less than two hours in the acidic and neutral medium. The accumulation of carbofuran in the human body causes health

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problems such as inhibition of acetylcholinesterase, diabetes, and cancer [9, 10].

Different traditional methods have been performed in water purification such as

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sedimentation, activated carbon, chlorination, coagulation, filtration, reverse osmosis

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etc, to control microorganisms that cause diseases and to eliminate odor, color and,

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unwanted taste, as well as toxic organic substance. However, some disadvantages

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have influenced their use such as, high cost, inability to degrade the recalcitrant organic compounds which require more treatments [11, 12]. Moreover, the emergence

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of new technologies with high efficiency, cheap, and have no negative effects on the environment. These new technologies called Advanced Oxidation Processes (AOPs)

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which includes photo-Fenton reaction [13], ozonation [14], photocatalytic oxidation [15], sonolysis [16], electrochemical oxidation [17] and ionizing radiation [18]. These

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technologies based on the generation of high potential oxidizing species such as hydroxyl radicals in sufficient quantities to convert all organic pollutants into low

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molecular weight compounds [19]. Among AOPs, UV/H2O2 is considering as one of the most preferred techniques in the removal of non-biodegradable organic compounds. The principle of this method based on the generation of hydroxyl radicals which initiate the decomposition of organic substances [20].

Several studies have been published on the degradation of carbofuran by AOPs [2123]. As carbofuran recalcitrant to the biodegradation method, this work is concentrated on its elimination by ultraviolet with and without hydrogen peroxide. The objective of this study is to evaluate the effect of irradiation time by UV on carbofuran removal and to determine the intermediates by-products. To best of our

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knowledge the measure of Formaldehyde, total acidity, pH and dissolved oxygen, by using UV and UV/H2O2 as advanced oxidation processes (APOs) for removal of

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carbofuran from the aqueous medium was not reported. Therefore this paper is

devoted for the investigation the change in these factors and to confirm the

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degradation of carbfuran in the aqueous medium using different UV irradiation time

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with and without hydrogen peroxide.

2. Materials and Methods

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2.1. Materials

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Carbofuran standard (98% purity), ammonium acetate (98% purity), acetic acid and oxalic acid were obtained from Sigma-Aldrich. Sodium nitrate, sodium nitrite, formic acid, sodium hydroxide (97% purity), hydrogen peroxide (H2O2) solution 30% (w/w)

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and methyl alcohol were supplied from Merck (Germany). Acetyl acetone (98% purity)

was

purchased

from

BDH

(poole,

England).

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trimethylsilyltrifluoro-acetamide (MSTFA) was obtained from Fluka. All chemicals and standards were used as received without any further purification. 2.2. UV- Photo-reactor

The photo chemical degradation process for carbofuran in aqueous solutions were carried out in UV-photo reactor, the reactor was situated in an axial position and encompassed by external jacket and water current was pumped to maintain the temperature of the solutions constant during experiment. The light source is a low pressure monochromatic mercury lamp with a power of 16 watt and 254 nm

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maximum emission wavelength. For all experiments, the reactor was loaded by 400 ± 1 mL aqueous solution of pesticide. Then the UV lamp was connected at the

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beginning of the experiments. All experiments were carried out at ambient temperature.

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2.3. Experimental procedure and Analytical techniques

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50 mgL-1 aqueous solutions of carbofuran were exposed to UV light with different

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irradiation time (15-240 min) without hydrogen peroxide. The experiments were

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performed with addition of hydrogen peroxide 4.8 ± 0.1 mM. The changes in wave length and characteristic peak for irradiated and unirradiated solutions were checked

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out by Varian Cary 100 UV–Vis spectrophotometer. pH and dissolved oxygen for irradiated and unirradiated solution were measured by NeoMet pH-200-L pH meter

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(ISTEK) and WAW Microprocessor Oximeter Oxi 3000, respectively. Titrimetric

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method was used to determine the total acidity. The intermediates formed during UVirradiation were identified by using the GC-MS (Thermo trace 1300, connected with ISQ LT single Quadruple mass spectrometer) using TG-SQC capillary column (15m x

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0.25mm x 0.25µm), injection was done in split less mode. The injector temperature was set at 275 °C and the temperature of the device is set at 80 °C. After waiting for 7 minutes in 80°C, it increases by 7°C per minute to reach 150°C, then increases by 7°C per minute to 200°C, and from 200°C to 275°C and finally held at 275◦C for 5 min. The injected amount into the device is 1 µL. The flow rate of helium gas is 1 mLmin-

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. The irradiated samples were concentrated by solid phase extraction by using Varian

C18 cartridge and collected pesticides were eluted by 2.0 mL methyl alcohol. The Ion Chromatography DX-3000 from Dionex, equipped with an electrochemical ultraanion self-regenerating suppressor model ASRS 300, 4 mm, a conductivity detector set at 100 mA and an AG9-HC guard column with an analytical column IonPac AS9-

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HC, columns-Dionex Ionpac AS9-HC and AG9-HC set at 30 ˚C was applied to determin the aliphatic acids. UV–Vis spectrophotometer and Hantzsch method were

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applied to determine the amount of formaldehyde formed during irradiation.

3. Results and Discussion

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3.1. Effect of H2O2 and evaluation of UV spectra The presence of H2O2 in aqueous solution during irradiation increases the formation

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of •OH radicals Eq. (1). However, any excess of hydrogen peroxide is counterproductive by the reaction of the peroxide with the hydroxyl radicals to form

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peroxide radicals which have no role in the removal process. Eq. (2). To avoid this and to increase the effectiveness of •OH radicals, the concentration of H2O2 was optimized at the level where its ability to produce hydroxyl radicals is higher than the scavenge processes. There are two possibilities for the presence of H2O2 in high

concentration, the first one complete mineralization of the contaminants or reducing the degradation by scavenging •OH radicals [24].

[HO• + HO• ] → 2HO•

(1)

H2 O2 + HO• → HO•2 + H2 O

(2)

H2 O2

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During irradiation in the presence of H2O2 in aqueous solution, the initial products are •OH radicals in the gas phase which surrounded by aqueous solvent molecules. This

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interaction between aqueous solvent molecules favors back recombination to form

H2O2 (2HO• → H2O2) Eq. (1). The recombination of OH radicals in the solvent causes to decrease the measured yield of the photolysis process in aqueous solution,

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and that reduces the diffusion of •OH for oxidation. The efficiency of photolysis is

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measured generally by the generation of •OH radicals [25, 26].

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The reaction mechanism of •OH formation depends on the concentration of H2O2

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during irradiation. The effects of hydrogen peroxide with UV irradiation time was

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examined on the degradation CBF, the concentration of H2O2 was set at 4.8 mM. Figs. 1 and 2 show the UV-Visible spectrum of irradiated solutions in the presence of 0.0

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and 4.8 mM H2O2. The obtained results illustrated that the efficiency of UV alone on the degradation of CBF is low but, the combination of UV irradiation with H2O2

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affected positively the degradation process. When applying the UV only the maximum removal percentage is about 11% for CBF. Generally, the utilization of UV irradiation alone did not affect sufficiently in the

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degradation of the pesticides. The maximum efficiency of 71% for CBF was done through the combination of UV and H2O2. Fig. 3 shows the results of the degradation percent. 3.2. Identification of Intermediate Species and Final Products

The •OH radical is a powerful oxidizing agent and non-selective in the interaction with organic compounds. Hence, numerous intermediates were formed after the treatment of aqueous solutions of carbofuran by UV in the presence and absence of H2O2. The GC-MS was used to determine the volatile by-products and other polar intermediates which required extracting in silyl ester and methyl alcohol. Fig.4 shows

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the chemical formula and retention time of the detected intermediates. 2,2-dimethyl-

2,3-dihydrobenzofuran-7-ol and ,2-dimethyl-2,3-dihydrobenzofuran-3,7-diol were

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formed due to the release of carbamate group at the beginning of hydrolysis when OH

attack the C-O bonds, 7-hydroxy-2,2dimethyl benzofuran-3(2H)-one was formed due

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to the hydroxylation of the furan ring by OH radicals, and pyrocatechol, was formed

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due to the opening rings in these intermediates and carbofuran. At 180 min UV

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irradiation in the presence of H2O2 the peaks of carbofuran and intermediates

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disappeared completely which means that carbofuran and intermediates have been

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converted into water and carbon dioxide.

3.3. Measurement of pH, total acidity, and dissolved oygen

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The pH, total acidity, and dissolved oxygen are the parameters that demonstrate the decomposition of pesticides. Fig. (5 a) shows the change in pH as a function of the

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irradiation time with and without hydrogen peroxide. The initial pH of the aqueous solution of CBF was 7.2 and after treatment, the pH declined to 3.57 with 4.8 mM H2O2 and 5.9 with 0.0 mM H2O2. This due to the consuming of •OH radical by the substrate and the production of acidic intermediates such as aliphatic acids. The increase in acidity with the irradiation time is due to the fragmentation products of the

benzene ring [27]. When we compared the change of pH and total acidity of CBF solutions (50 mgL-1) with the irradiation time, the results are agreeing with each other. An addition of 4.8 mM H2O2 to the solution caused a decrease in pH. This is due to the reaction of hydroxyl radicals with pesticide and the formation of photolytic products. When the total acidity increased, pH of CBF solutions decreased with the

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irradiation time. During the process of the radiation-induced degradation of CBF and the pH values of the solutions gradually decreased with the increasing irradiation.

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The amount of total acidity also was affected by the irradiation and H2O2. Fig. (5 b) shows the change in the concentration of irradiated CBF solutions it can be seen that

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the total acidity was increased with the irradiation time with and without H2O2 and

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this due to the formation of carboxylic acids which formed from the fragmentation of

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benzene rings [28].

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Since the dissolved oxygen is essential in the oxidation of organic compounds, it is expected to decrease during the degradation of carbofuran solutions by UV

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irradiation. Fig. (5 c) shows the change in dissolved oxygen in the presence and absence of H2O2 and the results illustrated that the dissolved oxygen was decreased with the irradiation doses increased. The decrease in dissolved oxygen during

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irradiation is due to the reaction between oxygen and reducing agent (H• and e‾aq) to form HO•2 and O•‾2. Radicals [29]. Eq (3) and (4) Also oxygen attack the carbon-

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centered radical and this reaction leads to the formation of aliphatic acids due to the fragmentation of the ring [27] Eq (5). This means that during water photolysis in the

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air more consuming of oxygen and more degradation of pollutants. e‾aq + O2 → O•‾ 2

(3)

H • + O2 → H2 O•

(4)

𝑅 • + 𝑂2 → 𝑅𝑂𝑂• → 𝑅 − 𝑂•

(5)

3.4. Evaluation of formaldehyde and aliphatic acids

Formaldehyde can be formed due to the decomposition of aromatic compounds by oxygen molecules during the irradiation. In this study, the formaldehyde was formed during the irradiation was determined by using the UV-Visible spectrophotometer. The absorption spectrum of formaldehyde complex was recorded at a wavelength of 412 nm. Fig. (6 d) shows the concentration of formaldehyde formed at the different

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irradiation times in the presence and absence of H2O2. In the presence of 4.8 mM

H2O2 the concentration of formaldehyde is slightly higher than 0.0 mM H2O2. The

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presence of hydrogen peroxide increases the generation of hydroxyl which plays an important role in the degradation of CBF.

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The irradiated solution of carbofuran was analyzed by ion chromatography to

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determine the amount and retention times of carboxylic acids and inorganic species

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formed during the irradiation of carbofuran. Fig.7 shows the concentration of these

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intermediate species. The three acids (acetic, formic, and oxalic) were detected and the results show that in the presence of hydrogen peroxide the amount of acids is

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higher than in the absence of hydrogen peroxide. Also, the amount of acids increased with the increasing irradiation time. These acids are formed due to the cleavage of

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aromatic rings by •OH radicals and oxygen molecules. Also, it is observed that formic acid was increased by the irradiation time at the maximum concentration at 60 min

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then began to decline rapidly and this is due to the fact that formic acid is the last stage of mineralization and then turns into water and carbon dioxide [30]. A small

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amount of nitrite was detected and the higher amount was found at 75 min and the release of nitrite during the irradiation was attributed to the reaction between •OH radicals and C-N bond in carbofuran and then the organic nitrogen converted into NO3‾ and NO2‾ [31]. 3.5. Degradation mechanism of Carbofuran in UV/H2O2 process

The purpose of oxidation of the toxic organic compounds by AOPs is to convert all carbon atoms and heteroatoms into low molecular weight compounds that are harmless to human and animal health such as CO2, H2O [32]. In this study, the intermediates and aliphatic acids were determined with GC-MS and ion chromatography. The intermediates were the same for both conditions (0.0 mM H2O2

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and 4.8 mM H2O2) except aliphatic acids observed for both conditions. The most

important one is the observation of nitrite after UV irradiation of carbofuran in the

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presence of hydrogen peroxide that records efficient mineralization. Fig.8 shows the suggested degradation mechanism of carbofuran when exposed to UV-irradiation.

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Initially, carbofuran is decomposed to aromatic intermediates which are 4-allyl-2-

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methoxyphenol, 4-(1-hydroxy-3-(methylamino)butan-2-yl)phenol, 2-(3,4-dime thoxy

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phenyl) acetic acid, 2,2-dimethyl-2,3-dihydrobenzofuran-7-ol, (E)-3-phenylbut-1-en-

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1-ol, 1-(benzo [d][1,3]dioxol-5-yl)propan-1-ol, 7-hydroxy-2,2-dimethylbenzo furan3(2H)-one, 1-(2-meth- oxyphenyl)-N-methylpropan-2-amine, and 2,2-dimethyl -2,3-

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dihydrobenzofuran-3,7-diol. These intermediates and carbofuran are transformed into common intermediate pyrocatechol. The mineralization proceeds on pyrocatechol by

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the formation of formic acid and acetic acid which degrade to oxalic acid, the last stage of mineralization. Nitrite ions are due to the degradation of 4-(1-hydroxy-3-

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(methylamino)butan-2-yl)phenol and Carbofuran. 4. Conclusion

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The decomposition of Carbofuran by UV irradiation was investigated. It was found that the contribution of UV alone in the degradation processes is very low. But, the combination of UV with hydrogen peroxide facilitates the degradation processes and the complete mineralization was obtained at 180 min, this due to the higher generation of OH radicals in the presence of H2O2. The possible degradation mechanism was

suggested depending on the intermediates and carboxylic acids which determined by GC-MS and ion chromatography. The decrease in the amount of dissolved oxygen and pH, increase in total acidity, and formaldehyde formation is one of the parameters that enhance the degradation of CBF by UV/H2O2. It has been demonstrated that the degradation of carbamate (carbofuran) pesticide in aqueous solutions is rapid and

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efficient by using UV irradiation-hydrogen peroxide processes. This has to be always considered in practical using of this technology for removal of carbofuran from

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drinking water and wastewater. Acknowledgments

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This research did not receive any specific grant from funding agencies in the public,

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commercial, or not-for-profit sectors. The experiments were performed and the

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facilities were used in Radiation Chemistry Laboratory at Hacettepe University,

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Ankara, Turkey. Khalid Elmamoun Ahmed Ibrahim would like to thanks Sudan Atomic Energy Commission, which allowed him to do this work at Hacettepe

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Fig 1. Absorption spectra of Carbofuran solutions as a function of UV irradiation

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time, [CBF]: 50 mg L-1, [H2O2]: 0.0 mM.

Fig 2. Absorption spectra of Carbofuran solutions as a function of UV irradiation time, [CBF]: 50 mgL-1, [H2O2]: 4.8± 0.1 mM.

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Fig 3. The percent degradation of CBF in water as a function of UV irradiation time

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in the absence and presence of H2O2, [CBF]: 50 mgL-1.

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4.8 mM H2O2 [CBF]: 50 mgL

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Irradiation time (min)

N

U

Irradiation time (min)

-1

SC R

7

0

1.5

0.0 mM H2O2

a

Total acidity (Mx10-4)

8

A

Fig 5. Change in the amount of a) pH, b) total acidity, c) dissolved oxygen, d)

M

formaldehyde as a function of UV irradiation time for carbofuran in the presence and

A

CC E

PT

ED

absence of H2O2, [CBF]: 50 mgL-1, [H2O2]: 4.8 mM.

[Acetic acid] (mgL-1)

4.8 mM H2O2 [CBF]: 50 mgL

-1

4

2

0 0

50

100

150

200

250

[Formic acid] (mgL-1)

0.0 mM H2O2

a

0.0 mM H2O2

b

4.8 mM H2O2 [CBF]: 50 mgL

6

3

0

300

0

50

Irradiation time (min) 0.0 mM H2O2 -1

6

3

0

50

100

150

200

200

250

300

250

4.8 mM H2O2

d

4.8 mM H2O2 [CBF]: 50 mgL

0

150

[CBF]: 50 mgL

0.2

0.1

0.0

300

-1

IP T

c

100

Irradiation time (min)

[Nirrite ions] (mgL-1)

[Oxalic acid] (mgL-1)

9

-1

0

50

Irradiation time (min)

100

SC R

6

150

200

250

300

Irradiation time (min)

U

Fig 6. Change in the amount of a) Acetic acid, b) Formic acid, c) Oxalic acid, d)

N

nitrite ions as a function of UV-irradiation time in the presence of 0.0 and 4.8 mM

A

CC E

PT

ED

M

A

hydrogen peroxide during the irradiation of Carbofuran (50 mgL-1) in water.

IP T SC R U N A M ED PT CC E A Fig 7. Suggested degradation mechanism of Carbofuran with UV-irradiation.